Frame for each job?

A lot of artists will use different machine frames for different purposes.
Typically a machine frame is made of iron, steel, brass,
aluminum, a metal-ceramic polymer, and even plastic. It is arguable
that the machine frame’s purity of metal content will assist
in creating a solid magnetic field. This magnetic field will help
the machine consistently run in the same manner. Lower grade
metals are argued to change in magnetic field strength the
longer they have electricity running through them. This would
alter the consistency at which the machine could optimally run in
theory.